1. Field of the Disclosure
This disclosure relates generally to apparatus and methods utilizing reflected waves in a fluid to induce vibrations downhole.
2. Background of the Art
Wellbores are drilled in subsurface formations for the production of hydrocarbons (oil and gas). Modern wells can extend to great well depths, often more than 15,000 ft. A wellbore is typically lined with casing (a string of metal tubulars connected in series) along the length of the wellbore to prevent collapse of the formation (rocks) into the wellbore. A number of operations are performed in the cased or open hole to prepare the wellbore for the production of hydrocarbons. Sometimes a device or a portion of a tool conveyed in the wellbore becomes trapped or stuck in the wellbore. The trapped device is often referred to as a “fish”. A variety of dislodging or fishing tools have been utilized to dislodge the trapped objects. Such tools are conveyed into the wellbore by a tubular and attached to the fish to dislodge the fish. Experiments have demonstrated that relatively low forces at higher frequencies are a more effective approach in retrieving a fish than traditional methods such as over-pulling or jarring. These conventional methods, in pulling a sand-lodged fish, can cause the sand grains to interlock and thereby wedge the fish more firmly in the wellbore.
The disclosure herein provides apparatus and methods that can transmit high frequency energy pulses to the fish, regardless of the depth at which the fish is lodged.